U.S. firearms agents told lawmakers on Wednesday they were instructed to only watch as hundreds of guns were bought, illegally resold and sent to Mexico where drug-related violence has raged for years.

Agents for the Bureau of Alcohol, Tobacco, Firearms and Explosives in Arizona told the House of Representatives Oversight Committee they were told not to arrest the so-called straw buyers and instead see where the guns went.

Republicans and Democrats on the panel expressed outrage about the ATF program — “Operation Fast and Furious” — and demanded answers from the Obama administration about why arrests were secondary to tracking the firearms.

“We monitored as they purchased handguns, AK-47 variants and .50 caliber rifles, almost daily at times,” John Dodson, an ATF special agent in Phoenix, told the committee.

“Rather than conduct any enforcement actions, we took notes, we recorded observations, we tracked movements of these individuals, we wrote reports but nothing more.”